It is known, for example, that highly pure aluminum oxide ceramics, for various electrical and electronic applications, are advantageously pretreated with an alkali solution or melt to improve their wettability and adhesion. In such a process, the surface of the ceramic material is disrupted, chemically inert surface regions are removed and a chemically active surface is produced. In addition, the surface is more or less roughened during this process so that mechanical anchoring is made possible, thereby permitting increased adhesion of the metal coating.
If surface roughening is not desirable, e.g., for electrical applications, an adhesion promoter is used. One such promoter is Cu.sub.2 O as disclosed in DE 2,533,524. Another promoter is silicic acid according to DE 2,004,133. Both these promoters are capable of reacting with a ceramic surface and simultaneously forming bonds with a copper layer.
It is also known to cover a ceramic surface by immersing the substrate in sensitizing and/or activating solutions with the use of, e.g., Sn/Pd catalyst nuclei, and subsequently covering the surface with copper by means of chemical deposition from copper baths which are commercially available. The steps of the known process are, in general, separate steps which are performed in succession. This process, however, is uneconomical, particularly for industrial mass production.
Thus, there is a need for an improved process of this type, whereby by combining various process steps into one, high adhesion of the applied metal layer and an economical as well as reliable manufacturing process is attained, which is particularly useful for industrial mass production.